Optical disc, optical disc recording method and apparatus, and optical disc reproducing method and apparatus

ABSTRACT

An optical disc that is reproducible by a reproducing apparatus has a still picture data and an audio data which are reproduced simultaneously. The still picture data is stored in a video part stream (ST1) comprising a plurality of units, and the audio data is stored in a second system stream (ST2) comprising one or a plurality of units. The units store time stamp information so that the second system stream (ST2) follows immediately after the video part stream (ST1). By changing the data in the second system stream (ST2), the audio data presented with a still picture can be freely and easily changed even after recording the still picture data using an MPEG standard format.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical disc for recording stillpicture data and audio data to be produced simultaneously with the stillpicture, an apparatus and a method for recording such an optical disc,and an apparatus and a method for reproducing such an optical disc.

2. Description of the Prior Art

Digital Cameras

Digital cameras for capturing still pictures using the JPEG compressionformat, formally known as the ISO/IEC 10918-1 standard, have becomewidely available in the last few years. One reason for the growingpopularity of digital cameras is the improved audio-visual (AV)processing capability of modern personal computers (PC).

Images captured by a digital camera can be transferred by various means,including semiconductor memory, floppy disk, and infraredcommunications, to a PC in a format enabling the image data to beprocessed and manipulated on the PC. The captured image data can then beedited on the PC for use by presentation programs, word processors, andby Internet content providers.

Digital cameras enabling audio to be captured with still pictures havebeen more recently introduced. This ability to capture sound with stillpictures has helped to further differentiate the digital camera fromconventional film-based still cameras.

FIG. 7 shows the relationship between still picture data (JPEG data) andaudio data recorded by such a digital camera. As shown in FIG. 7, thestill picture data (JPEG data) and audio data are stored in separatefiles. Each time a picture is taken (recorded), separate JPEG data andaudio data files are created.

There are two basic methods for managing the relationship between stillpicture data (JPEG data) and audio data files. The first, as shown inFIG. 7(a), uses a link manager to maintain the relationship (link)between a JPEG data file and the associated audio data file. The other,as shown in FIG. 7(b), assigns the same root file name (the part of thefile name minus the extension, e.g., "xyz" in FIG. 7(b)) to both theJPEG data file and the audio data file.

Using either of the above-described methods, an audio data file can belinked to a particular still picture data file when the picture iscaptured, and can be changed during any later editing process. That is,if the user decides after taking a picture that the audio associatedwith that picture is inappropriate or undesirable, different audio datacan be selected and linked to the image data on the PC.

The advent of MPEG (Moving Picture Experts Group) standards for handlingaudio-video data containing moving and still pictures together withaudio has also accelerated the development of multimedia products andservices based on MPEG standards.

When image data and audio are recorded using the MPEG standard, theaudio stream and video stream are multiplexed and recorded as a singlesystem stream as shown in FIG. 6(c). This makes it very difficult tofreely change the audio stream associated with a particular video streamafter the initial recording. More specifically, to change the audio datarecorded for a particular still picture, the still picture data andaudio data must be edited together as a single MPEG system stream. Thismeans that the MPEG system stream must first be decoded, and theextracted still picture data and audio data must then be re-encoded as asingle system stream after editing. Editing the still picture data andaudio data after recording is therefore much more difficult than it iswith a conventional digital camera.

SUMMARY OF THE INVENTION

An object of the present invention is therefore to provide a recordingmedium, an apparatus, and a method whereby audio data presented with astill picture can be freely and easily changed even after recording thestill picture data using an MPEG standard format.

To achieve the above object, a recording medium according to the presentinvention that is reproducible by a reproducing apparatus having adecoder buffer, decoder, and output section, has recorded thereto avideo part stream, such as a first system stream, (ST1) comprising aplurality of units containing still picture data for at least onepicture, and an audio part stream, such as a second system stream, (ST2)comprising one or a plurality of units containing audio data to bereproduced with the still picture data. The units of these systemstreams store time stamp information indicative of a time required for adecoding process and output. This time stamp information includes a timeSCR2 at which the last unit in the first system stream is input to adecoder buffer, and a time SCR3 at which the first unit in the secondsystem stream is input to a decoder buffer. These times SCR2 and SCR3are defined to satisfy the equation

    SCR2+Tp≦SCR3

where Tp is the time required to completely one unit to a decoderbuffer.

By the above arrangement, the second system stream carrying the audiodata is stored in the optical disc independently of the first systemstream. Thus, the data in the second system stream can be easilyrevised.

Preferably, the time stamp information further includes a time SCR1 atwhich the first unit in the first system stream is input to a decoderbuffer. In this case, times SCR1 and SCR2 are defined as:

    SCR1=0

    SCR2+Tp≦27000000 (27 MHz)

where (27 MHz) indicates that the numeric value shown therebefore is acount of a 27 MHz clock.

By this arrangement, the time period for transferring the first systemstream completely to the decoder buffer can be set to 1 second or less.

Yet further preferably in this case, time SCR3 is defined asSCR3=27000000 (27 MHz).

By this arrangement, the transfer start time of the second system streamto the decoder buffer can be set to 1 second after the start transfertime of the first system stream to the decoder buffer.

Yet further preferably, the time stamp information also includes a timePTS1 at which the first system stream is presented from the outputsection, and a time PTS3 at which the second system stream is outputfrom the decoder. In this case, times PTS1 and PTS3 are the same.

By this arrangement, the still picture produced by the first systemstream and the sound produced by the second system stream can beeffected simultaneously.

Yet further preferably, the time stamp information also includes adecoding start time DTS1 at which a decoder starts decoding the firstsystem stream. This time DTS1 is defined as:

    DTS1=90000 (90 kHz)

where (90 kHz) indicates that the numeric value shown therebefore is acount of a 90 kHz clock.

By this arrangement, the decode start time of the second system streamcan be set to 1 second after the start transfer of the first systemstream to the decoder buffer.

In this case, times PTS1 and PTS3 are preferably defined by theequation:

    PTS1=PTS3=90000(90 kHz)+Tv

where (90 kHz) indicates that the numeric value shown therebefore is acount of a 90 kHz clock, and Tv is the video data frame period.

By this arrangement, the presentation of the still picture and the soundcan be done after 1 second plus 1 frame period Tv from the starttransfer of the first system stream to the decoder buffer.

First and second system stream management information (Volumeinformation) is further preferably recorded to an optical disc accordingto the present invention, and the management information for the firstsystem stream includes an identification flag (Audio₋₋ Flag) fordeclaring there is audio data to be reproduced synchronized with thestill picture data.

By this identification flag, it is possible to detect whether or not thesound accompanies the still picture.

An optical disc recording apparatus for recording a system streamcontaining still picture data and audio data to be reproduced with thestill picture data to an optical disc according to the present inventioncomprises an encoder and a system controller. The encoder generates afirst system stream (ST1) comprising a plurality of units containingstill picture data for at least one picture, and a second system stream(ST2) comprising one or a plurality of units containing audio data to bereproduced with the still picture data. The system controller stores insaid units time stamp information indicative of a time required for adecoding process and output. The time stamp information includes a timeSCR2 at which the last unit in the first system stream is input to adecoder buffer, and a time SCR3 indicative of a time at which the firstunit in the second system stream is input to a decoder buffer. Thesetimes SCR2 and SCR3 are defined to satisfy the equation:

    SCR2+Tp≦SCR3

where Tp is the time required from the start to the end of inputting oneunit to a decoder buffer.

By the above arrangement, the second system stream carrying the audiodata is stored in the optical disc independently of the first systemstream. Thus, the data in the second system stream can be easilyrevised.

The system controller of this optical disc recording apparatus furtherpreferably stores as time stamp information a time SCR1 at which thefirst unit in the first system stream is input to a decoder buffer, anda time PTS1 at which the first system stream is output from the outputsection. These times SCR1, SCR2, and PTS1 are defined as:

    SCR1=0

    SCR2≦27000000 (27 MHz)-Tp

    PTS1=90000 (90 kHz)+Tv

where (27 MHz) indicates that the numeric value shown therebefore is acount of a 27 MHz clock, (90 kHz) indicates that the numeric value showntherebefore is a count of a 90 kHz clock, Tp is the time required totransfer the last unit of the first system stream, and Tv is the videodata frame period.

By this arrangement, the time for start transferring the first systemstream to the decoder buffer is set to 0, the time for finishtransferring the first system stream to the decoder buffer is set to 1second or less, and the time for displaying or presenting the stillpicture is set to 1 second plus 1 frame period Tv from the starttransfer of the first system stream to the decoder buffer.

Further preferably, the system controller further stores as time stampinformation a time PTS3 at which the second system stream is output fromthe decoder. In this case, times SCR3 and PTS3 are defined as:

    SCR3=27000000 (27 MHz)

    PTS3=90000 (90 kHz)+Tv.

By this arrangement, the time for transferring the second system streamto the decoder buffer can be set to 1 second from the strart transfer ofthe first system stream, and the time for decoding and reproducing thesound can be set to 1 second plus 1 frame period Tv.

The system controller further preferably generates first and secondsystem stream management information, and stores in the managementinformation for the first system stream an identification flag (Audio₋₋Flag). This flag is used for declaring whether there is audio data to bereproduced synchronized with the still picture data.

By this identification flag, it is possible to detect whether or not thesound accompanies the still picture.

The system controller yet further preferably records audio datareproduction time (Cell₋₋ Playback₋₋ Time) in the management informationfor the second system stream.

By this arrangement, it is possible to set the sound reproducing time.

An optical disc reproducing apparatus for reproducing an optical discaccording to the present invention comprises a decoder buffer, adecoder, an output section, and a system controller. When the systemcontroller detects that the identification flag (Audio₋₋ Flag) is set,it synchronously reproduces still picture data in the first systemstream and audio data in the second system stream.

By this arrangement, it is possible to previously detect whether or notthe sound accompanying the still picture exists.

Preferably, when the system controller detects that the identificationflag (Audio₋₋ Flag) is set, a decoder completely decodes one picture ofstill picture data recorded to the first system stream and sends thedecoded data to the output section, and another decoder then decodeswhile reproducing audio data stored to the second system stream. As aresult, presentation of still picture data from the output sectionbegins with the start of audio presentation.

By this arrangement, it is possible to decode the still picture data inthe first system stream and the audio data in the second system streamin separate time periods.

The present invention also provides an optical disc recording method forrecording a system stream containing still picture data and a separatesystem stream containing audio data to be reproduced with the stillpicture data to an optical disc according to the present invention.

In addition, the present invention also provides an optical discreproduction method for reproducing an MPEG stream recorded to anoptical disc according to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given below and the accompanying diagrams wherein:

FIG. 1 is a block diagram of a DVD recording apparatus drive;

FIGS. 2(a) and 2(b) show the relationship between address space on adisc and the amount of data stored in the track buffer;

FIGS. 3(a) and 3(b) show the correlation between I, B, and P pictures inan MPEG video stream;

FIG. 4 shows the structure of an MPEG system stream;

FIG. 5 is a block diagram of an MPEG system stream decoder (P₋₋ STD);

FIGS. 6(a), 6(b), 6(c) and 6(d) show video data, the change in theamount of data stored to the video buffer, a typical MPEG system stream,and an audio data signal, respectively, according to prior art;

FIGS. 7(a) and 7(b) illustrate links between still pictures and audio ina digital still camera, according to prior art;

FIGS. 8(a) and 8(b) are diagrams showing two different styles of adirectory structure and the physical arrangement of the disc recordingsurface;

FIGS. 9(a) and 9(b) show the structure of a management information file,and the data stream;

FIGS. 10(a), 10(b) and 10(c) show the management information data forstill picture data and audio data, a data stream for the still picturedata and audio data, and another data stream for the still picture dataand audio data;

FIGS. 11(a), 11(b) and 11(c) are diagrams showing a still picture dataVOB, an audio data VOB, and a combined VOB, according to the presentinvention;

FIG. 12 is a block diagram of a DVD recording apparatus;

FIG. 13 is a flow chart of a recording process of the DVD recordingapparatus shown in FIG. 12;

FIG. 14 is a flow chart of the still picture data VOB generating processshown as step S1301 in FIG. 13 in the DVD recording apparatus shown inFIG. 12;

FIG. 15 is a flow chart of the audio data VOB generating process shownas step S1303 in FIG. 13 in the DVD recording apparatus shown in FIG.12;

FIG. 16 is a flow chart of the management information file generatingprocess shown as step S1304 in FIG. 13 in the DVD recording apparatusshown in FIG. 12;

FIGS. 17(a) and 17(b) are explanatory views showing two still pictures;

FIGS. 18(a), 18(b), 18(c), 18(d) and 18(e) are diagrams showing anoperation according to the prior art to reproduce a still picture withan audio data;

FIGS. 19(a), 19(b), 19(c), 19(d) and 19(e) are diagrams showing anoperation according to the present invention to reproduce a stillpicture with single audio data; and

FIGS. 20(a), 20(b), 20(c), 20(d) and 20(e) are diagrams showing anoperation according to the present invention to reproduce a stillpicture with dual audio data.

DESCRIPTION OF PREFERRED EMBODIMENTS

The preferred embodiments of the present invention are described belowwith reference to the accompanying figures.

A preferred embodiment of the present invention is described below withreference to a DVD recording apparatus using DVD-RAM as the MPEG streamrecording medium.

1. Overview of a Normal MPEG Stream

A normal MPEG stream of audio-video data is described first below. Thestructure of the MPEG stream will be known to those with ordinaryknowledge of the related art, and the following description thereforefocuses on those parts having a particular relationship to the presentinvention.

As previously noted above, the MPEG standard defines an audio-videocompression method that has been formalized as the ISO/IEC 13818international standard.

The MPEG standard achieves high efficiency data compression primarily bymeans of the following two features.

First, moving picture data is compressed using a combination ofconventional intraframe compression using a spatial frequencycharacteristic to remove intraframe redundancy, and interframecompression using temporal correlations between frames to removeredundancy in adjacent frames. Even more specifically, the MPEG standardcompresses moving picture data by first categorizing each frame (alsoreferred to as a picture in MPEG parlance) as an I picture (intra-codedframe), P picture (a predictive-coded frame that is coded with referenceto a preceding picture), or a B picture (a bidirectionallypredictive-coded frame that is coded with reference to both a precedingand a following picture).

The relationship between I, P, and B pictures is shown in FIG. 3. Aswill be known from FIG. 3, P pictures are coded with reference to theclosest preceding I or P picture, and B pictures are coded withreference to the closest preceding and following I or P pictures. Asalso shown in FIG. 3, the picture display order and the coding order ofthe compressed data are different because each B picture is alsodependent on an I or P picture that is presented after the B picture.

The second feature of MPEG compression is dynamic (coding) dataallocation by picture unit based on image complexity. An MPEG decoderhas an input buffer for storing the input data stream, thus enabling alarge (coding) data size (that is, more data) to be allocated tocomplicated images that are more difficult to compress.

MPEG also supports MPEG audio, a separate MPEG encoding standard foraudio data to be reproduced with moving picture data. In addition,however, MPEG also supports the use of various other types of audioencoding for specific applications.

The present invention allows for two types of audio data encoding, thatis, encoding with data compression and encoding without datacompression. Exemplary audio encoding methods with data compressioninclude MPEG audio and Dolby(R) Digital (AC-3); linear pulse codemodulation (LPCM) is typical of audio encoding without data compression.Both AC-3 and LPCM are fixed bit rate coding methods. MPEG audio canselect from among several different bit rates on an audio frame unitbasis, although the range of bit rates is not as great as that availablefor video stream coding.

The MPEG system then multiplexes the encoded moving picture data andaudio data into a single stream, which is referred to as the MPEG systemstream. This multiplexed moving picture data and audio data is commonlyreferred to as AV data.

The structure of the MPEG system stream is shown in FIG. 4. As shown inFIG. 4, the MPEG system stream is a hierarchical structure of packs andpackets containing a pack header 41, packet header 42, and payload 43.

The packet is the smallest multiplexing unit, and the pack is thesmallest data transfer unit.

Each packet comprises a packet header 42 and payload 43. AV data isdivided into segments of an appropriate size starting from the beginningof the AV data stream, and these data segments are stored in the payload43. The packet header 42 contains a stream ID for identifying the typeof data stored to the payload 43, and a time stamp used for reproducingthe data contained in the payload 43. This time stamp is expressed with90 kHz precision. Data types identified by the stream ID include movingpicture and audio. The time stamp includes both a decoding time stampDTS and presentation time stamp PTS. The decoding time stamp DTS isomitted when decoding and presentation occur simultaneously, as withaudio data.

A pack typically contains a plurality of packets. In this preferredembodiment of the present invention, however, one pack contains onepacket. Thus, one pack comprises pack header 41 and one packet(comprising packet header 42 and payload 43) as shown in FIG. 4.

The pack header 41 contains a system clock reference SCR expressing with27 MHz precision the time at which the data in that pack is input to thedecoder buffer.

A decoder for decoding the above-noted MPEG system stream is describednext below.

FIG. 5 is a block diagram of a model MPEG system decoder (P₋₋ STD),particularly showing the detail of decoder 16. Shown in FIG. 5 are asystem controller 51 with a system time clock STC, an internal referenceclock for the decoder; a demultiplexer 52 for demultiplexing, that is,decoding, the system stream; a video decoder input buffer 53; videodecoder 54; a re-ordering buffer 55 for temporarily storing I and Ppictures in order to absorb the delay between the display order anddecoding order that occurs between I and P pictures and the dependent Bpictures; a switch 56 for adjusting the output sequence of the I, P, andB pictures in the re-ordering buffer 55; an audio decoder input buffer57; and an audio decoder 58.

The operation of this MPEG system decoder when processing an MPEG systemstream is described next.

When the time indicated by the STC 51 matches the system clock referenceSCR recorded in a pack header, the corresponding pack must be input tothe demultiplexer 52. Note that the STC 51 is initialized to the systemclock reference SCR at the first pack in the system stream. Thedemultiplexer 52 then interprets the stream ID in the packet header, andtransfers the payload data to the decoder buffer appropriate to eachstream. The demultiplexer 52 also extracts the presentation time stampPTS and decoding time stamp DTS. When the time indicated by the STC 51and the decoding time stamp DTS match, the video decoder 54 reads anddecodes the picture data from the video buffer 53. If the decodedpicture is a B picture, the video decoder 54 presents the picture. Ifthe decoded picture is an I or P picture, the video decoder 54temporarily stores the picture to the re-ordering buffer 55 beforepresenting the picture.

The switch 56 corrects the difference between the decoding sequence andthe presentation sequence as described above with reference to FIG. 3.That is, if a B picture is output from the video decoder 54, the switch56 is set to pass the video decoder 54 output directly from the systemdecoder. If an I or P picture is output from the video decoder 54, theswitch 56 is set to output the output from the re-ordering buffer 55from the system decoder.

It should be noted that I pictures cannot be simultaneously decoded andpresented because the picture sequence must be reordered to correct thedifferences between the decoding order and the display order. Even if noB pictures are present in the system stream, there is a delay of onepicture, that is, one video frame period, between picture decoding andpresentation.

Similarly to the video decoder 54, the audio decoder 58 also reads anddecodes one audio frame of data from the audio buffer 57 when the timeindicated by the STC 51 and the presentation time stamp PTS match (notethat there is no decoding time stamp DTS present in the audio stream).

MPEG system stream multiplexing is described next with reference to FIG.6. FIG. 6(a) shows several video frames, FIG. 6(b) represents the videobuffer state, FIG. 6(c) shows the MPEG system stream, and FIG. 6(d)shows the audio signal (audio data). The horizontal axis in each figurerepresents the time base, which is the same in each figure. The verticalaxis in FIG. 6(b) indicates how much data is stored in the video bufferat any given time; the solid line in FIG. 6(b) indicates the change inthe buffered data over time. The slope of the solid line corresponds tothe video bit rate, and indicates that data is input to the buffer at aconstant rate. The drop in buffered data at a regular period indicatesthat the data was decoded. The intersections between the diagonal dottedlines and the time base indicate the time at which video frame transferto the video buffer starts.

2. Problems with a Conventional MPEG Stream

Digital cameras using a conventional MPEG stream as described above arenot believed to be presently available as commercial products because ofthe problems described below. For the convenience of the followingdescription, however, it is herein assumed that this hypotheticaldigital camera exists.

The relationship between the reproduction operation of an MPEG streamdecoder in this hypothetical digital camera and the various time stamps(STC, PTS, DTS) is described first with reference to FIGS. 17 and 18.Note that the decoder is assumed to be comprised as shown in FIG. 5.

FIG. 17 is used to describe the operation for reproducing data capturedby the digital camera on a personal computer (PC). An exemplary screenpresented on the PC display is shown in FIG. 17(a). Photo #1 and photo#2 represent separate image files displayed on the screen in the form oficons. In a graphical user interface (GUI) such as Windows 95 (R),photos #1 and #2 may be presented as thumbnail sketches, for examples,which a user can click on using a mouse or other pointing device. The PCthen presents the file content corresponding to the photograph that wasclicked on by displaying the image on screen and outputting the audiofrom a speaker connected to the PC. FIG. 17(b) shows the contentdisplayed for photo #1 and photo #2 in this example.

When a user clicks on photo #1 in FIG. 17(a) in this example, stillpicture #1 is presented on screen, and audio #1 is output from the PCspeaker, as shown in FIG. 17(b). Likewise when the user clicks on photo#2, still picture #2 is presented on screen, and audio #2 is output fromthe PC speaker.

The relationship between decoder operation in this hypothetical digitalcamera and the various time stamps when photo #1 is reproduced is shownin FIG. 18 and described below.

The video output, still picture #1, and audio output, audio #1, that areoutput for photo #1 are shown in FIGS. 18(a) and 18(b). FIGS. 18(c) and18(d) show the change in the data stored to the video buffer 53 andaudio buffer 57 as still picture #1 and audio #1 are decoded and output.FIG. 18(e) shows the pack sequence and time stamps (SCR, PTS, DTS)stored in each pack when photo #1 is stored to disc as stream #1, whichis an MPEG stream in this example.

It should be noted that while not shown in the figure, the DTS and PTSare stored in the packet header of each packet as described above. Itwill also be obvious to one with ordinary skill in the related art thatwhile only four video packs and two audio packs are shown forsimplicity, there are actually more than 100 audio packs and video packseach because each pack is a maximum 2 KB.

The reproduction operation of this hypothetical digital camera starts bysending the packs contained in stream #1 shown in FIG. 18(e) to thedemultiplexer 52.

As shown in FIG. 18(e), stream #1 is multiplexed with the packs in thefollowing sequence, starting from the beginning of the stream: videopack V1, video pack V2, audio pack A1 video pack V3, video pack V4,audio pack A2. The pack header of each pack contains a system clockreference SCR, which indicates the timing at which that pack is input tothe demultiplexer 52. In the example shown in FIG. 18, time t1 is storedto system clock reference SCR #1 of video pack V1, time t2 is stored toSCR #2 of video pack V2, time t3 is stored to SCR #3 of audio pack A1,time t4 is stored to SCR #4 of video pack V3, time t5 is stored to SCR#5 of video pack V4, and time t6 is stored to SCR #6 of audio pack A2.

The PTS and DTS are also written to the first pack of each picture. Timet7 is thus written to PTS #1 of video pack V1, and time t6 is written toDTS #1. Note that the PTS and DTS are the same for every video pack in apicture, and are therefore not written to any but the first video pack.

The PTS is written to every audio pack. Therefore, time t7 is written toPTS #1 for audio pack A1, and time t9 is written to PTS #2 for audiopack A2. Note, further, that the PTS is written and the DTS is omittedin audio packs because the PTS and DTS are the same in an audio pack.The STC is reset at time t1, the value of SCR #1 in video pack V1, thatis, the first pack in stream #1, and each pack in the stream #1 is theninput to the demultiplexer 52 at the indicated by the SCR value in thepack header.

Therefore, as shown in FIG. 18(e), video pack V1 is input to thedemultiplexer 52 first at time t1, then video pack V2 is input at timet2, audio pack A1 is input at time t3, video pack V3 is input at timet4, video pack V4 is input at time t5, and audio pack A2 is input attime t8. Video packs input to the demultiplexer 52 are then output tothe video buffer 53, and audio packs are output to the audio buffer 57.

The second part of the reproduction operation of this hypotheticaldigital camera described below is the data decoding and output operationof the video packs output to the video buffer 53.

As shown in FIG. 18(c), while there is an ignorable delay between thevideo packs output from the demultiplexer 52, the video packs areaccumulated to the video buffer 53 at the system clock reference SCRtiming, that is, at time t1, t2, t4, and t5. Still picture #1 comprisesvideo packs V1 to V4. As a result, all video packs constituting stillpicture #1 have been stored to the video buffer 53 once video pack V4has been stored to the video buffer 53. As shown in FIG. 18(e), thedecoding time stamp DTS of still picture #1 comprising video packs V1 toV4 is time t6. The data accumulated to the video buffer 53 is thereforedecoded by video decoder 54 at time t6, and the data is cleared from thevideo buffer, thereby increasing the available buffer capacity.

The decoded video pack data of still picture #1 is an I picture. Thedecoded I picture is stored to re-ordering buffer 55, and is output fromthe decoder at PTS time t7.

Note that the end presentation time for still picture #1 is not definedby an MPEG stream time stamp. As a result, presentation typically endswhen reproduction of the next MPEG stream begins, or when video outputis terminated by a control command sent to the decoder from anotherapplication or device. The example shown in FIG. 18 therefore showspresentation of still picture #1 continuing even after time t10, thetime at which audio output ends.

The third part of the reproduction operation of this hypotheticaldigital camera described below is the relationship between the timestamps and the operation whereby audio pack data output to the audiobuffer 57 is decoded and output.

As shown in FIG. 18(d), the audio packs output from the demultiplexer 52are stored to the audio buffer 57 at time t3 and t8, thus increasing theamount of data stored to the audio buffer 57. Unlike the video data, thePTS and DTS are the same in the audio data. As a result, audio data isoutput at the same time the audio decoder 58 [57, sic, and below]decodes the audio pack data. More specifically, the audio pack A1 datastored to audio buffer 57 is decoded by audio decoder 58 at thepresentation time stamp PTS, i.e., time t7, and audio output begins. Theaudio pack A2 data stored to the audio buffer 57 at time t8 is thendecoded and output at the PTS, that is, time t9, by audio decoder 58.

The time that data can be stored to each decoder buffer is also limitedin the MPEG system. This limit is 1 sec. in the case of moving picturedata. This means that the maximum difference between the transfer timesof simultaneously output audio and video data, that is, the maximum SCRdifference, is 1 second. However, a delay equal to the time required toreorder the video data may also occur.

3. MPEG Stream Problems

Through years of research and development, the inventors have identifiedand organized problems presented by the conventional MPEG streamdescribed above with respect to using the MPEG stream in a digital stillpicture camera.

As noted above, the MPEG system stream contains video data and the audiodata presented with that video data multiplexed into a single systemstream. Editing this system stream to change the audio presented with aparticular video image is therefore difficult once the audio and videostreams have been multiplexed into a single system stream. This meansthat when a digital camera uses an MPEG stream to encode and store astill picture and the audio recorded when that picture was taken to arecording medium, it is difficult to later edit the audio to replace theaudio recorded when the picture was taken with a different audio signal.

Referring to the example shown in FIG. 17, when photo #1 is captured bya digital still picture camera, photo #1 is recorded by the camera to adisc or other recording medium as an MPEG stream multiplexing stillpicture #1, that is, the still picture data, and audio #1, that is, theaudio data captured at the same time. The resulting MPEG stream thuscomprises multiplexed video packs and audio packs as shown in FIG.18(e). As a result, after the user takes a picture, it is difficult tochange the audio data of photo #1 from audio #1 to a different audiosignal.

Though difficult, the following three methods of editing the audio dataafter recording are conceivable.

(1) Generate a plurality of MPEG streams, each multiplexing the videodata (the photographed still picture data) with one of a plurality ofaudio data streams that might be used with the video data, and recordall of these plural MPEG streams to the recording medium. This methodmeans that in the example shown in FIG. 18, a number of other streams,each containing the same video packs but a different selection of audiopacks, is recorded in addition to stream #1 shown in FIG. 18(e). Thereis a limit to the number of MPEG streams that can be recorded, however,because the storage capacity of the recording medium is also limited.More particularly, however, it is not practically possible for the userto record at the time the picture is taken all audio data that might bedesirably combined with the still picture.

(2) Decode the MPEG stream during editing to separate the still picturedata from the audio data, and then re-encode the system stream with thestill picture data and the new audio data. This method, however,requires system stream decoding and encoding each time the audio isedited, thus increasing the required editing time. The entire systemstream is also stored as decoded (uncompressed) data, thus requiring alarge amount of memory in the digital camera.

(3) Record the video stream and audio stream as two separate(unmultiplexed) streams, and determine what audio stream to use with aparticular video stream at the time of reproduction. This method makesit possible to add audio data after recording a still picture to therecording medium, and then reproduce the added audio data whenreproducing the still picture.

The inventors of the present invention have used the above method (3).More specifically, the present invention provides a method and apparatusfor reproducing two MPEG streams stored separately on disc as thoughthey are a single MPEG stream using a conventional MPEG decoder.

MPEG Stream According to the Present Invention

To achieve the present invention by using a conventional decoder toreproduce two separate MPEG streams, one for still picture data and onefor audio data, as noted above, it is necessary to drive the decoder toprocess the two MPEG streams as a single system stream.

The first problem to be overcome in processing two MPEG streams asthough they are a single system stream is that a discrete time stamp isassigned to the two streams. When the two streams are processedcontinuously as one stream, contradictions such as a discontinuitybetween the time stamps assigned to the two streams can occur.

While the time stamps in the MPEG stream are multiplexed into the data,the initial time stamp value (the first system clock reference SCR inthe stream) in a normal MPEG stream is not defined by the MPEG standard.In practice, therefore, the encoder assigns a specific value.

It will therefore be obvious that there is no continuity or correlationbetween the time stamps assigned to MPEG streams generated by differentencoders. Assume, for example, that encoder A generates an MPEG stream Aencoded with an initial SCR of 0, and an encoder B generates an MPEGstream B encoded with an initial SCR of 1000. The SCR of the last packin stream A is 27000000 (27 MHz). Here, (27 MHz) indicates that thenumber preceding (27 MHz) is a counted value using 27 MHz clock. StreamsA and B are to be continuously processed by the decoder as a singlestream. A discontinuity occurs in the SCR in this case between the endof stream A and the beginning of stream B, and there is a strongpossibility that the decoder hangs up or other error occurs.

To resolve this problem, a recording apparatus according to the presentinvention limits the values of the time stamps (SCR, PTS, DTS) in thesystem streams that are generated and recorded to disc.

The MPEG stream time code limits imposed by the present invention aredescribed next below.

FIG. 11 is referred to below to describe the time stamps used for thestill picture data system stream ST1 and the audio data system streamST2 in this preferred embodiment of the present invention.

FIG. 11(a) shows the structure of the system stream for still picturedata, referred to as a video object (VOB). System clock reference SCR1is written to the pack header of the first pack in the VOB, and PTS1 andDTS1 are written to the packet header of the first VOB. SCR2 is writtento the pack header of the last pack.

FIG. 11(b) shows the VOB for the audio data system stream ST2. SCR3 iswritten to the pack header of the first pack in this VOB, and PTS3 iswritten to the packet header.

FIG. 11(c) shows the sequence in which the still picture data and audiodata system streams are input continuously to the decoder duringreproduction.

In order to drive the decoder to process the still picture data systemstream ST1 and audio data system stream ST2 as a single system stream,the values assigned to the system clock reference SCR2 in the last packof the still picture data system stream ST1, and the system clockreference SCR3 in the first pack of the audio data system stream ST2,are limited as defined by equation (1) below in the present invention.

    SCR2+Tp≦SCR3                                        (1)

where Tp is the time required to transfer one pack to the decoder. Morespecifically, Tp is a time period from the moment when one pack startsto enter the demultiplexer 52 until said one pack completely enters thedemultiplexer 52. Since the pack merely passes through the demultiplexer52, it is also possible to say that Tp is a time period from the momentwhen one pack starts to enter the buffer 53 (or 57) unit said one packcompletely enters the buffer 53 (or 57).

It should be noted that equation (1) limits the smallest value that canbe assigned to SCR3. SCR3 is often set to zero (0) in a conventionalMPEG stream. A recording apparatus according to the present invention,however, calculates the SCR3 value from equation (1).

By thus calculating the value of SCR3, SCR2 is prevented from beinggreater than SCR3, and the SCR values in each pack of the still picturedata system stream ST1 and audio data system stream ST2 are assured ofbeing in a rising numerical sequence from one system stream to the next.

Equation (1) also assures that the difference between SCR2 and SCR3 isat least Tp. This prevents the transfer timing of the first pack in theaudio data system stream ST2 from conflicting with the transfer of thelast pack in the still picture data system stream ST1, that is,transferring the first pack in the audio data system stream ST2 will notstart while the last pack in the still picture data system stream ST1 isstill being transferred.

It should be further noted that if the system stream transfer rate is 8Mbps, the pack transfer time TP will be 55296 (27 MHz); if 10.08 Mbps,the pack transfer time Tp will be 43885 (27 MHz).

A decoder according to the present invention is further comprised toaccept input of the audio data system stream ST2 following a stillpicture data system stream ST1 without first resetting the STC afterinput thereto of a still picture data MPEG stream has been completed.This is because it would be meaningless to limit the value of the SCR inthe first audio stream pack if the decoder resets the STC after stillpicture data input, as it conventionally does after each system stream.

By thus driving the decoder to process supplied system streams based ontime stamp values calculated as described above, the decoder can handleseparate still picture data and audio data system streams as a singleMPEG stream. That is, a still picture data stream and a separatelyrecorded audio data stream can be reproduced as though they are a singlesystem stream.

The presentation time stamps PTS1 and PTS3 are also set to the samespecified value as shown in equation (2) below.

    PTS1=PTS3=specified value                                  (2)

This assures that both audio and still picture data output begin at thesame time.

In this exemplary embodiment of the present invention, this specifiedvalue is

    90000 (90 kHz)+Tv

where Tv is the video frame period, and (90 kHz) indicates that thenumber preceding (90 kHz) is a counted value using 90 kHz clock. In anNTSC signal, Tv is therefore 3003; in a PAL signal, it is 3600.

The time stamps shown in FIG. 11 are described more specifically belowwith reference to a case in which still picture data and audio outputbegin simultaneously at approximately 1 second (90000 (90 kHz)+Tv) afterdata reading based on the time stamps calculated from the aboveequations (1) and (2).

The time stamp for the still picture data VOB is described first.

(1) The system clock reference SCR (SCR1) for the first pack in thestill picture data VOB is 0 (27 MHz).

(2) The decoding time stamp DTS (DTS1) for the first pack in the stillpicture data VOB is 90000 (90 kHz). Note that a still picture data VOBcontains only one still picture.

(3) The presentation time stamp PTS (PTS1) for the first pack in thestill picture data VOB is 93003 (90 kHz). Note that PTS1=93003 is for anNTSC video signal; for a PAL video signal, PTS1=93600. This is becausethe video frame period (Tv) in an NTSC signal is 3003, and is 3600 in aPAL signal. Note, further, that because a still picture data VOBcontains only one still picture, all packs are output simultaneously atthe time indicated by PTS1.

(4) The SCR (SCR2) of the last pack in the still picture data VOB is setto a value 27000000 (27 MHz) minus the transfer time of one pack (Tp).

The value 27000000 (27 MHz) is called a base value below.

This base value is set so that the longest delay between when movingpicture data is input to the decoder buffer and when it is decoded is 1second (27000000 (27 MHz)).

More specifically, if the maximum moving picture data storage time isapplied to still picture data, all packs in the still picture data VOBmust be transferred to the decoder within 1 second (27000000 (27 MHz)).If SCR1 for the first pack is 0, the data stored in the first pack willbe decoded within 1 second (27000000 (27 MHz)) after it is transferredto the decoder, and the SCR (SCR2) of the last pack in the same stillpicture data VOB is therefore pack transfer time Tp less than 27000000(27 MHz).

The PTS value and this base value are defined as described above toensure encoder compatibility. In other words, if the still picture datasystem stream ST1 and audio data system stream ST2 are encoded using thevalues derived from equations (1) and (2), the above specified PTSvalue, and the above base value, the present invention can be appliedregardless of what encoder generates the system streams.

It should be noted that the base value is defined in this preferredembodiment as 27000000 (27 MHz). The following equations (3) and (4) cantherefore be derived where this base value is MaxT.

    SCR2+Tp≦MaxT                                        (3)

    SCR3=MaxT                                                  (4)

The time stamps of the audio data VOB are described next.

(1) The system clock reference SCR (SCR3) of the first audio pack is27000000 (27 MHz). Using this value, the audio pack will be input to thedecoder continuously to the preceding still picture data VOB at theshortest time satisfying equation (1). In addition, because the stillpicture data PTS1 is 93003 (90 kHz), the SCR must be set to a smallervalue in order to simultaneously output the audio.

(2) The presentation time stamp PTS (PTS3) of the first audio frame inthe VOB is 93003 (90 kHz). As noted above, this is for an NTSC videosignal; if PAL video, PTS3 is 93600.

It will also be obvious to one with ordinary skill in the related artthat insofar as the still picture data VOB and audio data VOB areencoded to satisfy equations (1) and (2), the present invention shallnot be limited to the conditions (values) described above.

For example, if the video is an NTSC signal and the first SCR is27000000 (27 MHz) rather than 0, the following values apply.

SCR1=27000000 (=1 sec)

SCR2≦53944704 (=SCR3-Tp)

SCR3=54000000 (=SCR1+1 sec)

PTS1=PTS3=183003 (=DTS1+3003)

DTS1=180000 (=1 sec)

If the video is an NTSC signal, the first SCR is 0, and PTS is 1 second,the following values apply.

SCR1=0

SCR2≦26043804 (=SCR3-Tp)

SCR3=26099100 (=1 sec-3003×300)

PTS1=PTS3=90000 (=1 sec)

DTS1=86997 (=PTS1-3003)

If the video is a PAL signal and the first SCR is 27000000 (27 MHz), thefollowing values apply.

SCR1=27000000 (=1 sec)

SCR2≦53944704 (=SCR3-Tp)

SCR3=54000000 (=SCR1+1 sec)

PTS1=PTS3=183600 (=DTS1+3600)

DTS1=180000 (=1 sec)

If the video is a PAL signal, the first SCR is 0, and PTS is 1 second,the following values apply.

SCR1=0

SCR2≦25864704 (=SCR3-Tp)

SCR3=25920000 (=1 sec-3600×300)

PTS1=PTS3=90000 (=1 sec)

DTS1=86400 (=PTS1-3600)

If the transfer rate is 10.08 Mbps, and the video is an NTSC signal, thefollowing values apply.

SCR1=0

SCR2≦26956115 (=SCR3-Tp (=43885))

SCR3=27000000 (=1 sec)

PTS1=PTS3=93003 (=DTS1+3003)

DTS1=90000 (=1 sec)

If the transfer rate is 10.08 Mbps, and the video is a PAL signal, thefollowing values apply.

SCR1=0

SCR2≦26956115 (=SCR3-Tp (=43885))

SCR3=27000000 (=1 sec)

PTS1=PTS3=93600 (=DTS1+3600)

DTS1=90000 (=1 sec)

An operation whereby an MPEG stream having time stamps defined asdescribed above is processed by an exemplary decoder is described nextbelow with reference to FIG. 19 and FIG. 20. Note that this decoder iscomprised as shown in FIG. 5.

Like FIG. 18, FIG. 19 shows the relationship between decoder operationin digital still camera according to the present invention and thevarious time stamps when photo #1 is reproduced.

The video output, still picture #1, and audio output, audio #1, that areoutput for photo #1 are shown in FIGS. 19(a) and 19(b). FIGS. 19(c) and19(d) show the change in the data stored to the video buffer 53 andaudio buffer 57 as still picture #1 and audio #1 are decoded and output.FIG. 19(e) shows the pack sequence and the time stamps (SCR, PTS, DTS)written to each pack of the video stream #1 and audio stream #1, both ofwhich are MPEG streams, when photo #1 is stored to disc as two streams#1 and #2.

It should be noted that the packet structure and further descriptionthereof are omitted here as in FIG. 18.

The first part of the description of the reproduction operation of adigital still camera according to the present invention starts with theoperation for transferring the packs of streams #1 and #2 shown in FIG.19(e) to the demultiplexer 52.

As shown in FIG. 19(e), stream #1 comprises video pack V1, video packV2, video pack V3, and video pack V4 multiplexed in sequence from thebeginning of the stream. Stream #2 likewise comprises audio pack A1 andaudio pack A2 multiplexed in sequence starting from the beginning of thestream. It is important to note here that stream #1 comprises only videopacks, and stream #2 comprises only audio packs.

The pack header of each pack also contains a system clock reference SCR.As shown in FIG. 19(e), SCR#1 of video pack V1 in stream #1 is time t1;SCR#2 of video pack V2 is time t2; SCR#3 of video pack V3 is time t3;and SCR#4 of video pack V4 is time t4. The presentation time stamp PTSand decoding time stamp DTS are also set in the first video pack in thevideo stream V1. PTS#1 in video pack V1 is time t8, and DTS#1 is timet6.

In this preferred embodiment as described above, the value of time t1,that is, the value of SCR#1 in the first video pack V1, is 0. The valueof SCR#4 in the last video pack V4 is likewise 27000000 (27 MHz)-Tp,where Tp is the pack transfer time described above and is 55296 (27MHz). Assuming that the video data is NTSC coded, time t8 of PTS#1 is93003 (90 kHz), and time t6 of DTS#1 is 90000 (90 kHz).

The system clock reference SCR#5 of the first audio pack A1 in stream #2is time t7, and SCR#6 of audio pack A2 is time t9. A presentation timestamp PTS is also set in audio packs A1 and A2. PTS#5 in audio pack A1is time t8, and PTS#6 in audio pack A2 is time t10.

In this preferred embodiment as described above, the value of time t7,that is, the value of SCR#5 in the first audio pack A1, is 27000000 (27MHz). Time t8 of PTS#5 in audio pack A1 is the same as the video dataPTS, that is, 93003 (90 kHz).

The system time clock STC is reset to time t1, the value of SCR#1 in thefirst video pack V1, and each pack in stream #1 is then input to thedemultiplexer 52 at the time indicated by the SCR of each pack.

That is, as shown in FIG. 19(e), the first video pack V1 is input to thedemultiplexer 52 at time t1, video pack V2 is input at time t2, videopack V3 at time t3, and video pack V4 at time t4.

The decoding process of a digital still camera according to the presentinvention differs from a conventional camera as described with referenceto FIG. 18 in that the system time clock STC of the decoder is not resetafter all of stream #1 is input, and the packs of stream #2 are inputcontinuously to the demultiplexer 52 at the SCR timing written to eachpack.

The first audio pack A1 in stream #2 is thus input to the demultiplexer52 at time t7, and audio pack A2 is input at time t9.

It is important to note here that the SCR#4 of the last video pack V4and the SCR#5 of the first audio pack A1 are set to satisfy equation (1)above, which can thus be restated as follows.

    SCR#4+Tp≦SCR#5                                      (1)

Continuity between the SCR values of stream #1 and stream #2 is thusassured, the interval therebetween is at least equal to the packtransfer time, and the decoder can thus continuously process two streamswithout hanging up.

The demultiplexer 52 outputs video packs input thereto to the videobuffer 53, and outputs audio packs input thereto to the audio buffer 57.

The second part of the reproduction operation of a digital cameraaccording to the present invention described below is the data decodingand output operation of the video packs output to the video buffer 53.

As shown in FIG. 19(c), while there is an ignorable delay between thevideo packs output from the demultiplexer 52, the video packs areaccumulated to the video buffer 53 at the SCR timing, that is, at timet1, t2, t3, and t4. Still picture #1 comprises video packs V1 to V4. Asa result, all video packs constituting still picture #1 have been storedto the video buffer 53 once video pack V4 has been stored to the videobuffer 53. As shown in FIG. 19(e), the decoding time stamp DTS of stillpicture #1 comprising video packs V1 to V4 is time t6. The dataaccumulated to the video buffer 53 is therefore decoded by video decoder54 at time t6, and the data is cleared from the video buffer, therebyincreasing the available buffer capacity.

The decoded video pack data of still picture #1 is an I picture. Thedecoded I picture is stored to re-ordering buffer 55, and is output fromthe decoder at PTS time t8.

The third part of the reproduction operation of a digital cameraaccording to the present invention described below is the relationshipbetween the time stamps and the operation whereby audio pack data outputto the audio buffer 57 is decoded and output.

As shown in FIG. 19(d), the audio packs output from the demultiplexer 52are stored to the audio buffer 57 at time t7 and t9, thus increasing theamount of data stored to the audio buffer 57. Unlike the video data, thePTS and DTS are the same in the audio data. As a result, audio data isoutput at the same time the audio decoder 58 [57, sic, and below]decodes the audio pack data. More specifically, the audio pack A1 datastored to audio buffer 57 is decoded by audio decoder 58 at thepresentation time stamp PTS, i.e., time t8, and audio output begins. Theaudio pack A2 data stored to the audio buffer 57 at time t9 is thendecoded and output at the PTS, that is, time t10, by audio decoder 58.

It is important to note here that the PTS is the same in the stillpicture data stream #1 and the audio data stream #2. As a result, stream#1 and stream #2 are input to the decoder at different times, but areoutput at the same time, which is determined by the PTS.

It will therefore be obvious that insofar as the time stamps are withinthe limits defined above, an MPEG stream comprising only still picturedata, and an MPEG stream comprising only audio data, can be processedcontinuously, one following the other, by a decoder, with the audio andvideo presentation occurring simultaneously.

It will also be obvious that by recording the still picture data MPEGstream and audio data MPEG stream separately to disk, the audio to bereproduced with a particular still picture can be freely and easilychanged and edited after the still picture data is captured andrecorded.

Assume, for example, that still picture #1 and audio #1 described abovewith reference to FIG. 19 are the data recorded to disk when the imagewas photographed. To later change the audio that is to be outputsimultaneously with the still picture #1, it is only necessary to recordan MPEG stream encoded with time stamps derived from equations (1) and(2). An example of this new audio #2 additionally recorded as MPEGstream #3 is shown in FIG. 20.

Though not shown in the figures, management information indicating whataudio data MPEG stream is to be reproduced simultaneously with the MPEGstream for still picture #1 is also recorded to disk. This managementinformation can then be updated so that the MPEG stream for audio #2 isreproduced simultaneously with the MPEG stream for still picture #1instead of the MPEG stream for audio #1.

DVD-RAM Description

DVD-RAM is described next below as a recording medium and recordingformat suitable for recording MPEG streams as described above.

Advances in high density recording technologies for rewritable opticaldiscs have expanded their range of applications from computer data andmusic to image data. A typical conventional optical disc has a guidechannel of either lands or grooves formed on the signal recordingsurface of the disc. This has meant that signals are recorded using onlythe lands or the grooves. The development of a land and groove recordingmethod, however, has enabled signals to be recorded to both lands andgrooves, thus approximately doubling the recording density of the disc.

Constant linear velocity (CLV) control is also an effective means ofimproving recording density, and the development of a zoned CLV controlmethod has made it easier to implement CLV control.

How to utilize these high capacity optical discs to record AV data,including video and other image data, and achieve new products withfeatures and functions far surpassing those of conventional AV productsis a major concern for the industry.

It is also thought that the availability of large capacity, rewritableoptical disc media will result in the primary medium for recording andreproducing AV materials changing from conventional tape media tooptical disc media. The change from tape to disc media will also havewide-ranging effects on the functions and performance of AV equipment.

One of the greatest benefits to be gained from a switch from tape todisc media is a significant increase in random access performance. Whileit is possible to randomly access tape media, several minutes may berequired to access a particular part of the tape due to the need tofast-forward and/or rewind in a linear fashion. When compared with theseek time of optical disc media, which is typically on the order ofseveral 10 milliseconds, there is an obvious and significant improvementin random access performance achieved by a switch to disc media. Tape istherefore obviously unsuitable as a random access medium.

Random access also means that distributed (that is, non-contiguous)recording of AV material is possible with optical disc media, thoughimpossible with conventional tape media.

Logic Structure of DVD-RAM Media

The logic structure of DVD-RAM media is described next below withreference to FIG. 8. FIG. 8(a) shows the directory file and theorganization of the disc recording area.

The recording area of the optical disc is arranged into a plurality ofphysical sectors in a spiral pattern from the inside circumference tothe outside circumference of the disc.

The physical sectors of the disc are further allocated to one of threeareas from the inside circumference to the outside circumference of thedisc. A lead-in area is located at the inside circumference area of thedisc. A lead-out area is located at the outside circumference area ofthe disc. A data area is provided between the lead-in and lead-outareas.

Each sector also has an address segment and a data segment. The addresssegment stores address information specifying the location of thatsector on the optical disc, and an identifier identifying whether thesector is in the lead-in, data, or lead-out area. Digital data is storedto the data segment.

The data segment of sectors in the lead-in area contains information forinitializing the device used to reproduce data from the disc(reproduction device). This information typically includes a referencesignal required for servo stabilization, and an ID signal fordifferentiating one disc from another.

The data segment of sectors in the data area records the digital dataconstituting the application [? or user data ?] stored to the disc.

The lead-out area identifies the end of the recording area for thereproduction device.

Management information for managing disc content and constituting thefile system is recorded to the beginning of the data area. Thismanagement information is the volume information. The file system is atable of contents for grouping a plurality of disc sectors into groups,and managing these disc sector groups. A DVD-RAM medium according to thepresent invention preferably uses the file system defined in ISO 13346.

An optical disc according to this preferred embodiment has a filedirectory structured as shown in FIG. 8(a).

All data handled by a DVD recording apparatus belongs to the VIDEO₋₋ RTdirectory directly under the ROOT directory.

There are two basic file types handled by a DVD recording apparatus: asingle management information file, and at least one, though typicallyplural, AV files.

Management Information File

The content of the management information file is described next withreference to FIG. 9(a).

The management information file contains a VOB (video object) table anda PGC (program chain) table. A VOB is an MPEG program stream. Theprogram chain defines the reproduction order of individual cells. A cellis a logic unit for reproduction, and corresponds to a particular partor all of a VOB. In other words, a VOB is a meaningful unit in an MPEGstream, and the PGC is unit reproduced by an MPEG stream reproducingapparatus.

The VOB table records the number of VOBs (Number₋₋ of₋₋ VOBs), andcertain information about each VOB. This VOB information includes: thename of the corresponding AV file (AV₋₋ File₋₋ Name); the VOB identifier(VOB₋₋ ID); the start address in the AV file (VOB₋₋ Start₋₋ Address);the end start address in the AV file (VOB₋₋ End₋₋ Address); the VOBplayback time (VOB₋₋ Playback₋₋ Time); and stream attributes (VOB₋₋Attribute).

The PGC table records the number of PGCs (Number₋₋ of₋₋ PGCs) [Number₋₋of₋₋ VOBs, sic], and certain information about each PGC. This PGCinformation includes: the number of cells in the PGC (Number₋₋ of₋₋Cells), and certain cell information.

This cell information includes: the corresponding VOB₋₋ ID; the cellstart time in the VOB (Cell₋₋ Start₋₋ Time); the cell playback time inthe VOB (Cell₋₋ Playback₋₋ Time); the address at which cell playbackstarts in the VOB (Cell₋₋ Start₋₋ Address) and the address at which cellplayback ends (Cell₋₋ End₋₋ Address); an audio flag indicating thatthere is audio to be reproduced simultaneously with the still picturedata (Audio₋₋ Flag). When Audio₋₋ Flag is set to 1, cell extensioninformation exists for the related audio data, that is, the VOB₋₋ ID,Cell₋₋ Start₋₋ Time, Cell₋₋ Playback₋₋ Time, Cell₋₋ Start₋₋ Address, andCell₋₋ End₋₋ Address. When Audio₋₋ Flag is reset to 0, cell extensioninformation for the related audio data does not exist.

It is important here to note the audio flag (Audio₋₋ Flag), which isused to declare whether or not there is audio data to be outputsimultaneously with the still picture.

AV File

The AV file structure is described next with reference to FIG. 9(b).

An AV file has at least one, and typically plural, VOBs. VOBs arerecorded continuously to disc, and VOBs associated with a particular AVfile are arranged contiguously on disc. VOBs in an AV file are managedusing the VOB info in the management information file. When the DVDreproducing apparatus first accesses the management information file, itreads the VOB start and end addresses, and is thus able to access theVOB.

The logical reproduction unit of the VOB is the cell. A cell is a partof the VOB to be reproduced; it may correspond to the entire VOB, andcan be set as desired by the user. These cells make editing simplewithout actually manipulating the AV data. As with a VOB, cell access ismanaged using the cell information in the management information file. ADVD reproducing apparatus thus accesses the management information fileto read the cell start and end address information in order to access acell.

Cell address information is referenced to the VOB, and VOB addressinformation is referenced to the AV file. As a result, the DVDreproducing apparatus accesses a cell by adding the cell addressinformation to the VOB address information to calculate the address inthe AV file, enabling the DVD reproducing apparatus to access the AVfile.

Links between Still Picture Data and Audio Data

How a still picture and audio are synchronously reproduced is describednext with reference to FIG. 10.

FIG. 10(a) shows part of the management information file describedabove. As shown in FIG. 10(a), cell information for a still picturecontains access information (VOB₋₋ ID, Cell₋₋ Start₋₋ Time, Cell₋₋Playback₋₋ Time, Cell₋₋ Start₋₋ Address, and Cell₋₋ End₋₋ Address) forthe still picture data and the corresponding audio data.

The audio flag (Audio₋₋ Flag) declares whether there is audio data to bereproduced with the still picture data. Therefore, when the audio flagindicates that there is audio data to be reproduced with the stillpicture data, the cell also contains access information for the audiodata VOB.

A relationship between still picture data and audio data is thusestablished by setting the audio flag (Audio₋₋ Flag) and declaring theVOB information for the audio data.

FIG. 10(b) shows an AV file for still picture data and audio data. Datastored in a VOB is either still picture data or audio data. There is noVOB that contains both still picture data and audio data in amultiplexed manner. Unlike moving picture data VOBs, in the presentinvention, still picture data VOBs comprise only a single I picturevideo frame, an intraframe compressed video image, and audio data VOBscontain only audio data. The still picture data and audio data playbackcontrol information is generated by referring to the cell informationfor the still picture data VOBs and audio data VOBs, and defining thestill picture cell playback order from the PGC.

It is therefore possible to freely combine still picture data and audiodata streams by defining the playback order of referenced cells forseparately recorded still picture data and audio data.

It should be noted that while this preferred embodiment has beendescribed as having two VOBs for one MPEG stream; one for the video dataand the other for the audio data, the data structure is not limited assuch as long as the audio data and the video data can be separated, andthe separated audio data can be replaced with another audio data.

For example, the video data (video stream part) and the audio data(audio stream part) can be incorporated in a single VOB. Such an exampleis shown in FIG. 10(c). In this case, the video data of the stillpicture is stored in the video part, which is located in the leadinghalf portion of the VOB, and the audio data is stored in the audio part,which is located in the trailing half portion of the VOB. FIG. 10(c)shows RTR₋₋ STO.VRO file, such as shown in FIG. 8(b).

It is noted that the first system stream ST1 shown in FIG. 11 and thevideo part shown in FIG. 10(c) are generally referred to as a video partstream. Similarly, the second system stream ST2 shown in FIG. 12 and theaudio part shown in FIG. 10(c) are generally referred to as an audiopart stream.

The file structure may also be as shown in FIG. 8(b). In this case, theV1DEO₋₋ RT directory corresponds to the DVD₋₋ RTR directory, andRTR.IFO, RTR₋₋ STO.VRO, RTR₋₋ STA.VRO, and RTR₋₋ MOV.VRO files are underthe DVD₋₋ RTR directory.

The RTR.IFO file corresponds to the management information file. TheRTR₋₋ STO.VRO and RTR₋₋ STA.VRO files are related to the still picturedata. The RTR₋₋ STO.VRO file records the still picture data (video part)and the audio data (audio part) simultaneously recorded with the stillpicture data. The RTR₋₋ STA.VRO file records only the audio data (audiopart) edited after initial recording. Audio data in the RTR₋₋ STA.VROfile is recorded with a relationship to still picture data recorded inthe RTR₋₋ STO.VRO file. Moving picture data is recorded separately fromstill picture data in the RTR₋₋ MOV.VRO file.

Still Picture Data VOB and Audio Data VOB

As described above with reference to FIG. 11, the time stamps for thestill picture data VOBs and audio data VOBs are as shown below.

SCR1=0

SCR2≦27000000 (27 MHz)-Tp

SCR3=27000000 (27 MHz)

Tp=55296 (27 MHz)

PTS1=PTS3=90000+Tv

DTS1=90000

Description of a DVD Recording Apparatus

A DVD recording apparatus is described next.

FIG. 1 is a block diagram of a DVD recording apparatus. Shown in FIG. 11are: an optical pickup 11 for reading data from and writing data to adisc; an error correction code (ECC) processor 12; a track buffer 13; aswitch 14 for changing input to and output from the track buffer 13; anencoder 15; and a decoder 16. Reference numeral 17 is an enlarged viewof the disc surface.

As shown in enlarged view 17, the smallest recording unit for datarecorded to a DVD-RAM disc is the sector, which holds 2 KB. One ECCblock contains 16 sectors, and is the unit processed by the ECCprocessor 12 for error correction.

Using a track buffer 13 enables AV data recorded at non-contiguouslocations on the disc to be supplied to the decoder without aninterruption in the data stream. This is described below with referenceto FIG. 2.

FIG. 2(a) shows the address space on the disc. When the AV data isrecorded to two separate contiguous regions, [a1, a2] and [a3, a4] asshown in FIG. 2(a), continuous presentation of the AV data can bemaintained while seeking address a3 from a2 by supplying dataaccumulated to the track buffer to the decoder. This is illustrated inFIG. 2(b).

When reading AV data from address al starts at time t1, the data isinput to the track buffer with output from the track buffer beginning atthe same time. There is, however, a difference of (Va-Vb) between thetrack buffer input rate Va and the output rate Vb from the track buffer.This means that data gradually accumulates in the track buffer at therate (Va-Vb). This continues to address a2 at time t2. If B(t2) is theamount of data accumulated in the track buffer at time t2, the dataB(t2) stored in the track buffer can be supplied to the decoder untilreading begins again from address a3 at time t3.

More specifically, if the amount of data read from [a1, a2] before theseek operation begins is at least equal to a predetermined amount, i.e.,at least equal to the amount of data supplied to the decoder during theseek operation, AV data can be supplied without interruption to thedecoder.

It should be noted that the still picture data system stream ST1 andaudio data system stream ST2 processed contiguously by the decoder inthe present invention is not necessarily contiguously recorded to thedisc. In the case shown in FIG. 20, for example, there are two audiodata system streams, streams #2 and #3, that can be processedcontinuously with the still picture data system stream ST1 #1 by thedecoder. It will be obvious that only one of these audio data systemstreams can be recorded contiguously to the still picture data systemstream ST1 on disc, and the other audio data system stream ST2 must berecorded at an address that is non-contiguous to stream #1.

A DVD recording apparatus comprised as described above, however, canstill supply two non-contiguous streams to the decoder with nointerruption between the streams. The decoder can therefore continuouslyprocess two streams, and the operation described with reference to FIG.19 can be assured.

It should be further noted that while the above example has addressedreading, that is, reproducing data from DVD-RAM, the same principleapplies to writing, that is, recording data to DVD-RAM.

More specifically, insofar as a predetermined amount of data is recordedcontiguously to DVD-RAM, continuous reproduction and recording arepossible even if the AV data is recorded non-contiguously.

FIG. 12 is a block diagram of a DVD recording apparatus.

Shown in FIG. 12 are: a user interface 1201 for presenting messages tothe user and receiving commands from the user; a system controller 1202for overall system control and management; an input section 1203,typically a camera and microphone; an encoder 1204, including a videoencoder, audio encoder, and system stream encoder; an output section1205, typically comprising a monitor and speaker; a decoder 1206,including a system stream decoder, audio decoder, and video decoder; atrack buffer 1207; and a drive 1208.

The recording operation of a DVD recording apparatus thus comprised isdescribed next below with reference to the flow charts in FIG. 13, FIG.14, and FIG. 15.

Operation starts when a user command is received by the user interface1201. The user interface 1201 passes the user command to the systemcontroller 1202. The system controller 1202 interprets the user command,and appropriately instructs the various modules to perform the requiredprocesses. Assuming that the user request is to capture a still pictureand record the accompanying audio, the system controller 1202 instructsthe encoder 1204 to encode one video frame and encode the audio.

The encoder 1204 thus video encodes and then system encodes the onevideo frame sent from the input section 1203, thus generating a stillpicture data VOB. The encoder 1204 then sends this still picture dataVOB to the track buffer 1207. (S1301)

This still picture data VOB encoding process is described morespecifically below with reference to FIG. 14.

The encoder 1204 first initializes the various time stamps. In thisexample, it resets the system clock reference SCR to 0, and initializesthe PTS and DTS to 93003 (90 kHz) and 90000 (90 kHz), respectively.(S1401) Note that if PAL video is used, the PTS is initialized to 93600(90 kHz).

If still picture data recording is not completed, the encoder 1204converts the still picture data to a pack and packet structure. (S1404)

Once the pack and packet structure is generated, the encoder 1204calculates the SCR, DTS, and PTS time stamps, and inserts these valuesto the pack and packet stream of still picture data. (S1405) Note thatthe SCR of the first pack is set to the initialization value of 0, andthe PTS and DTS are set to the initialization values of 93003 (90 kHz)and 90000 (90 kHz), respectively. The SCR of the last pack in the streamis forced to a time stamp earlier than 27000000 (27 MHz) minus the packtransfer time Tp.

The encoder 1204 then loops back to S1402, and determines whether stillpicture data recording has finished. If it has, the encoder 1204notifies the system controller 1202 that still picture data VOBgeneration has been completed. The system controller 1202 then controlsthe drive 1208 to record the still picture data VOBs stored to the trackbuffer 1207 to the DVD-RAM disc. (S1403)

It will also be obvious to one with ordinary skill in the related artthat while a DVD recording apparatus according to this preferredembodiment of the invention records to DVD-RAM disc after all stillpicture data VOBs have been generated, recording can proceed parallel tostill picture data VOB generation to record the VOBs as they aregenerated.

Returning to FIG. 13, after still picture data encoding is completed,the encoder 1204 determines whether there is an audio recording toencode. If there is, it begins encoding the audio data sent from theinput section 1203, and sequentially transfers the generated audio dataVOBs to the track buffer 1207. (S1302, S1303)

This audio data encoding process is described more specifically belowwith reference to FIG. 15.

The encoder 1204 first initializes the SCR and PTS time stamps. In thisexample, it sets the system clock reference SCR to 27000000 (27 MHz),and initializes the PTS to 93003 (90 kHz). Note that if thesimultaneously presented still picture is PAL video, the PTS isinitialized to 93600 (90 kHz). (S1501)

If audio data recording is not completed, the encoder 1204 converts theaudio data to a pack and packet structure (S1504), and calculates andinsets the SCR and PTS time stamps (S1505). In this example, the SCR ofthe first pack is set to the initialization value of 27000000 (27 MHz),and the PTS is set to 93003 (90 kHz).

The encoder 1204 then loops back to S1502, and determines whether audiodata recording has finished. If it has, the encoder 1204 notifies thesystem controller 1202. The system controller 1202 then controls thedrive 1208 to record the audio data VOBs stored in the track buffer 1207to the DVD-RAM disc. (S1503)

It will also be obvious to one with ordinary skill in the related artthat while a DVD recording apparatus according to this preferredembodiment of the invention records to DVD-RAM disc after all audio dataVOBs have been generated, recording can proceed parallel to audio dataVOB generation to record the VOBs as they are generated.

The DVD recording apparatus continues recording still picture data andaudio data to the DVD-RAM disc using the above-described recordingmethod until the user stops stream recording.

A stop recording command from the user is applied to the systemcontroller 1202 from the user interface 1201. The system controller 1202thus sends a stop recording command to the encoder 1204, and controlsthe drive 1208 to record the remaining VOBs in the track buffer 1207 tothe DVD-RAM disc.

After completing the above-described sequence, the system controller1202 generates a management information file containing a VOB table andPGC table as shown in FIG. 9(a), and drives the drive 1208 to record themanagement information file to the DVD-RAM disc. (S1304)

Decision diamond S1305 then determines whether audio data was recorded.If it was, the audio flag (Audio₋₋ Flag) is set to 1 in this example(S1306); if there was no audio data, the audio flag (Audio₋₋ Flag) isreset to 0 in this example (S1307).

The management information is also set to adjust the cell playback time(Cell₋₋ Playback₋₋ Time) for the still picture data and audio data tothe audio playback time.

The recording method according to the present invention as describedabove thus records to DVD-RAM disc still picture data and audio data inwhich the time stamps are assigned to predetermined values.

The playback (reproducing) apparatus of the DVD recording apparatus isdescribed next below with reference to FIG. 12 and the flow chart inFIG. 16.

Operation starts when a user command is received by the user interface1201. The user interface 1201 passes the user command to the systemcontroller 1202. The system controller 1202 interprets the user command,and appropriately instructs the various modules to perform the requiredprocesses. Assuming that the user request is to play the disc, thesystem controller 1202 controls the drive 1208 to read the PGC tablecontaining the playback order from the management information file.

The system controller 1202 then determines specific PGC informationbased on the PGC table read from disc. Following the playback orderindicated by the PGC information, the system controller 1202 reproducesthe corresponding VOBs. More specifically, the PGC information containsthe cell playback order. Each cell contains a VOB₋₋ ID and VOB start andend address information. This cell information is what enables accessingthe still picture data VOBs. (S1601)

The system controller 1202 then determines the state of the audio flag(Audio₋₋ Flag) in the still picture data cell to be reproduced. (S1602)

If the audio flag (Audio₋₋ Flag) is set (=1), the system controller 1202reads the extended audio VOB information, that is, the VOB₋₋ ID and VOBstart and end addresses, from the still picture data cell information toread both the still picture data VOB and the audio data VOB to besimultaneously reproduced. (S1603)

As described above, the cell address information is referenced to theVOB, and VOB address information is referenced to the AV file. Inpractice, therefore, the VOB address information is added to the celladdress information to calculate the address in the AV file that is usedby the DVD reproducing apparatus to access and read AV data recorded tothe DVD-RAM disc. (S1604)

It should be noted that if the audio flag (Audio₋₋ Flag) is not set(i.e., is reset to 0), that is, only still picture data is to bereproduced with no audio, the still picture data is presented for thetime indicated by the Cell₋₋ Playback₋₋ Time stored in the managementinformation file.

The decoder process for continuously processing still picture data VOBsand audio data VOBs when the audio flag (Audio₋₋ Flag) is set (=1) isdescribed more specifically below.

That is, the system controller 1202 first reads a still picture data VOBinto the track buffer 1207, and if the audio flag (Audio₋₋ Flag) is set,instructs the decoder 1206 to decode the still picture data VOBs duringthe time needed to read the audio data VOB into the track buffer 1207.The decoder 1206 is instructed to begin decoding as soon as audio dataVOB reading starts. The decoder 1206 thus reads MPEG streams stored tothe track buffer 1207, and passes the decoded data to the output section1205. The output section 1205 outputs data received from the decoder1206 to the monitor and speaker at the presentation time specified inthe data.

By thus first reading and decoding still picture data as describedabove, image data and audio data can be reproduced synchronized to aspecified presentation time once audio data reading begins.

It is important to note here that the decoder 1206 is able to process asingle still picture and accompanying audio data as a single VOB byconstructing still picture data VOBs and audio data VOBs as describedabove.

It should also be noted that while the present invention has beendescribed above with reference to a DVD-RAM disc, it can also be usedwith other types of media. The present invention shall therefore not belimited to DVD-RAM discs and other types of optical discs.

Furthermore, the present invention has been described using by way ofexample an audio stream as the stream to be simultaneously reproducedwith the still picture data system stream ST1. The invention shall notbe so limited, however, and other types of information that can beoutput with a still picture data system stream ST1 can be alternativelyused. For example, a secondary image system stream comprising bitmappeddata or text data can also be used. A typical application for such asecond image system stream is to provide captions or subtitles displayedsuperimposed on the photographed still picture.

Yet further, the present invention has been described using the cell asthe unit for linking still picture data and audio data. Alternatively,one cell could be equal to one VOB, and the still picture data and audiodata could be linked in VOB units.

Yet further, the present invention has been described using same thecell playback time (Cell₋₋ Playback₋₋ Time) information in the stillpicture data and audio data. The cell playback time, however, need notnecessarily be the same. For example, the audio data information couldbe given priority such that when the reproducing apparatus reads adifferent cell playback time (Cell₋₋ Playback₋₋ Time) it ignores theplayback information for the still picture data.

Yet further, the present invention has been described with the stillpicture data VOBs and audio data VOBs recorded to an AV file separatelyfrom other VOBs. The present invention does not impose any limits on theAV file structure, however, and still picture data VOBs and audio dataVOBs can be recorded with other VOBs in the same AV file.

Advantages of the Invention

In an optical disc to which at least still picture data and audio dataare recorded to separate recording areas as MPEG streams having a packand packet structure, the time at which input of the last pack of stillpicture data to the decoder buffer starts (system clock reference SCR2),and the time at which input of the first pack of audio data to thedecoder buffer starts (system clock reference SCR3), are recorded bymeans of the present invention to satisfy the equation

    SCR2+Tp≦SCR3

where Tp is the time required to transfer one pack to the decoderbuffer.

This makes it possible to decode separately recorded still picture dataand audio data system streams as though they are a single MPEG stream.

In addition, by recording the time at which input of the first pack ofstill picture data to the decoder buffer starts (SCR1), the time atwhich input of the last pack of still picture data to the decoder bufferstarts (SCR2), and the time at which input of the first pack of audiodata to the decoder buffer starts (SCR3), to the following values:

SCR1=0

SCR2+Tp≦27000000 (27 MHz)

SCR3=27000000 (27 MHz)

still picture data and audio data encoded by different encoders canstill be decoded as though they are a single MPEG stream.

Furthermore, by recording the [still picture] data presentation starttime (PTS1) and audio data presentation start time (PTS3) as the samevalues, still picture data can be presented synchronized to the audiodata, that is, presentation can begin simultaneously.

In addition, by defining the still picture data presentation start time(PTS1) and audio data presentation start time (PTS3) as follows:

    PTS1=PTS3=90000 (90 kHz)+Tv

the decoder can synchronously reproduce even still picture data andaudio data encoded by different encoders.

Yet further, by setting an identification flag (Audio₋₋ Flag) fordeclaring the presence of audio data to be synchronously reproduced inthe management information of still picture data, an optical discreproducing apparatus can determine whether there is audio data to bereproduced, and still picture data and audio data can thus besynchronously reproduced.

Although the present invention has been described in connection with thepreferred embodiments thereof with reference to the accompanyingdrawings, it is to be noted that various changes and modifications willbe apparent to those skilled in the art. Such changes and modificationsare to be understood as included within the scope of the presentinvention as defined by the appended claims, unless they departtherefrom.

What is claimed is:
 1. An optical disc that is reproducible by areproducing apparatus having a decoder buffer, decoder, and outputsection, said optical disc having recorded theretoa video part streamcomprising a plurality of units containing still picture data for atleast one picture, and an audio part stream comprising one or aplurality of units containing audio data to be reproduced with the stillpicture data; wherein said units store time stamp information indicativeof a time required for a decoding process and output, said time stampinformation includes a time SCR2 indicative of a time at which the lastunit in the video part stream is input to a decoder buffer, and a timeSCR3 indicative of a time at which the first unit in the audio partstream is input to a decoder buffer, and said times SCR2 and SCR3 aredefined to satisfy the following equation:

    SCR2+Tp≦SCR3

where Tp is the time required from the start to the end of inputting oneunit to a decoder buffer.
 2. The optical disc as set forth in claim 1,wherein the time stamp information further includes a time SCR1indicative of a time at which the first unit in the video part stream isinput to a decoder buffer, and times SCR1 and SCR2 are defined asfollow:SCR1=0 SCR2+Tp≦27000000 (27 MHz)where (27 MHz) indicates that thenumeric value shown therebefore is a count of a 27 MHz clock.
 3. Theoptical disc as set forth in claim 1, wherein time SCR3 is definedas:SCR3=27000000 (27 MHz).
 4. The optical disc as set forth in claim 1,wherein the time stamp information further includes:time PTS1 indicativeof a time at which the video part stream is output from the outputsection; time PTS3 indicative of a time at which the audio part streamis output from the decoder; and times PTS1 and PTS3 are the same.
 5. Theoptical disc as set forth in claim 1, wherein the time stamp informationfurther includes:decoding start time DTS1 indicative of a time at whicha decoder starts decoding the video part stream; and time DTS1 isdefined as:

    DTS1=90000 (90 kHz)

where (90 kHz) indicates that the numeric value shown therebefore is acount of a 90 kHz clock.
 6. The optical disc as set forth in claim 4,wherein times PTS1 and PTS3 are defined by the following equation:

    PTS1=PTS3=90000 (90 kHz)+Tv

where (90 kHz) indicates that the numeric value shown therebefore is acount of a 90 kHz clock, and Tv is the video data frame period.
 7. Theoptical disc as set forth in claim 1, wherein video and audio partstream management information is further recorded to the optical disc,andmanagement information for the video part stream includes anidentification flag for declaring there is audio data to be reproducedsynchronized with the still picture data.
 8. An optical disc recordingapparatus for recording a system stream containing still picture dataand audio data to be reproduced with the still picture data to anoptical disc that is reproducible by a reproducing apparatus having adecoder buffer, decoder, and output section, said optical disc recordingapparatus comprising:an encoder, and a system controller; said encodergenerating a video part stream comprising a plurality of unitscontaining still picture data for at least one picture, and an audiopart stream comprising one or a plurality of units containing audio datato be reproduced with the still picture data; said encoder storing insaid units time stamp information indicative of a time required for adecoding process and output; wherein the time stamp information includesa time SCR2 indicative of a time at which the last unit in the videopart stream is input to a decoder buffer, and a time SCR3 indicative ofa time at which the first unit in the audio part stream is input to adecoder buffer, and said times SCR2 and SCR3 are defined to satisfy thefollowing equation:

    SCR2+Tp≦SCR3

where Tp is the time required from the start to the end of inputting oneunit to a decoder buffer.
 9. The optical disc recording apparatus as setforth in claim 8, wherein the encoder further stores as time stampinformation:a time SCR1 indicative of a time at which the first unit inthe video part stream is input to a decoder buffer, and a time PTS1indicative of a time at which the video part stream is output from theoutput section, wherein times SCR1, SCR2, and PTS1 are defined asfollow:SCR1=0 SCR2≦27000000 (27 MHz)-Tp PTS1=90000 (90 kHz)+Tvwhere (27MHz) indicates that the numeric value shown therebefore is a count of a27 MHz clock, (90 kHz) indicates that the numeric value showntherebefore is a count of a 90 kHz clock, Tp is the time required totransfer the last unit of the video part stream, and Tv is the videodata frame period.
 10. The optical disc recording apparatus as set forthin claim 9, wherein the encoder further stores as time stampinformation:a time PTS3 indicative of a time at which the audio partstream is output from the decoder; and times SCR3 and PTS3 are definedas follow:SCR3=27000000 (27 MHz) PTS3=90000 (90 kHz)+Tv.
 11. The opticaldisc recording apparatus as set forth in claim 8, wherein the systemcontroller generates video and audio part stream management information,and stores in the management information for the video part stream anidentification flag for declaring there is audio data to be reproducedsynchronized with the still picture data.
 12. The optical disc recordingapparatus as set forth in claim 8, wherein the system controller recordsaudio data reproduction time in the management information for the audiopart stream.
 13. An optical disc reproducing apparatus for reproducingan optical disc as set forth in claim 7, said optical disc reproducingapparatus comprising:a decoder buffer; a decoder; an output section; anda system controller; wherein when the system controller detects that theidentification flag is set, the system controller synchronouslyreproduces still picture data in the video part stream and audio data inthe audio part stream.
 14. The optical disc reproducing apparatus as setforth in claim 13, wherein when the system controller detects that theidentification flag is set,a decoder completely decodes one picture ofstill picture data recorded to the video part stream and sends thedecoded data to the output section; a decoder then decodes whilereproducing audio data stored to the audio part stream; and presentationof still picture data from output section begins with a start of audiopresentation.
 15. An optical disc recording method for recording asystem stream containing still picture data and audio data to bereproduced with the still picture data to an optical disc that isreproducible by a reproducing apparatus having a decoder buffer,decoder, and output section, said optical disc recording methodcomprising:a video part stream recording step for recording a video partstream comprising a plurality of units containing still picture data forat least one picture; an audio part stream recording step for recordingan audio part stream comprising one or a plurality of units containingaudio data to be reproduced with the still picture data; and a timestamp information recording step for recording time stamp informationindicative of a time required for a decoding process and output to saidunits; wherein the time stamp information includes a time SCR2indicative of a time at which the last unit in the video part stream isinput to a decoder buffer, and a time SCR3 indicative of a time at whichthe first unit in the audio part stream is input to a decoder buffer,and said times SCR2 and SCR3 are defined to satisfy the followingequation:

    SCR2+Tp≦SCR3

where Tp is the time required from the start to the end of inputting oneunit to a decoder buffer.
 16. The optical disc recording method as setforth in claim 15, wherein the time stamp information further includes:atime SCR1 indicative of a time at which the first unit in the video partstream is input to a decoder buffer, and a time PTS1 indicative of atime at which the video part stream is output from the output section,wherein times SCR1, SCR2, and PTS1 are defined as follow:SCR1=0SCR2≦27000000 (27 MHz)-Tp PTS1=90000 (90 kHz)+Tvwhere (27 MHz) indicatesthat the numeric value shown therebefore is a count of a 27 MHz clock,(90 kHz) indicates that the numeric value shown therebefore is a countof a 90 kHz clock, Tp is the time required to transfer the last unit ofthe video part stream, and Tv is the video data frame period.
 17. Theoptical disc recording method as set forth in claim 16, wherein the timestamp information further includes:a time PTS3 indicative of a time atwhich the audio part stream is output from the decoder; and times SCR3and PTS3 are defined as follow:SCR3=27000000 (27 MHz) PTS3=90000 (90kHz)+Tv.
 18. The optical disc recording method as set forth in claim 15,further comprising:a management information recording step for recordingmanagement information for the video and audio part streams, andgenerates in the management information for the video part stream anidentification flag for declaring there is audio data to be reproducedsynchronized with the still picture data.
 19. The optical disc recordingmethod as set forth in claim 18, wherein an audio data reproduction timeis further stored in the management information for the audio partstream.
 20. An optical disc reproduction method for reproducing an MPEGstream recorded to an optical disc as set forth in claim 7, said opticaldisc reproduction method comprising:a detection step for detectingwhether an identification flag for declaring there is audio data to bereproduced synchronized with the still picture data is set in themanagement information of still picture data for a single picture; and aplayback step for synchronously reproducing still picture data and audiodata according to the detected state of the identification flag.
 21. Theoptical disc reproduction method as set forth in claim 20, wherein theplayback step for synchronously reproducing still picture data and audiodata comprises:a decoding step for completing decoding still picturedata for one picture according to the detected state of theidentification flag; a reproducing step for then decoding andreproducing the audio data; wherein reproducing decoded still picturedata starts simultaneously to a start of audio presentation.